Video: How Antidepressants Work in the Brain

Depression leads to feelings of sadness. It's thought that the mood disorder is influenced by lower than normal concentrations of certain neurotransmitters within the brain. Learn how antidepressants increase these feel-good neurotransmitters.2015-08-10

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Depression leads to feelings of sadness. It's thought that the mood disorder is influenced by lower than normal concentrations of certain neurotransmitters within the brain. Learn how antidepressants increase these feel-good neurotransmitters.

Depression

Depression is a disorder characterized by feelings of hopelessness, sadness and a lack of interest in life. Despite the fact that this mood disorder is common in places like the United States, the definitive cause is not well understood.

This lack of understanding may stem from the fact that depression can have multiple contributing factors, including a genetic propensity toward the disorder, hormonal imbalance and emotional upset. Regardless of the factors that lead a person to feel depressed, the medical community agrees that an underlying alteration in the brain's chemistry plays a role. In this lesson, we will explore how the brain is affected by depression and how antidepressants work to prevent and treat depression.

How the Brain Works

From the outside, the human brain looks like an unimpressive mass of bumpy tissue. However, inside, there's a lot of chemical activity happening among countless nerve cells, or neurons. The balance of chemicals being exchanged between these neurons directs your thoughts, affects your mood and influences your emotions. Specific chemicals, known as neurotransmitters, act as chemical messengers that allow neurons to communicate with each other.

When one nerve wants to send a message to another nerve, the first nerve releases neurotransmitters into a gap that separates the two nerves. Some of these neurotransmitters get transferred to the second nerve, and any remaining neurotransmitters get reabsorbed back into the first nerve. Certain neurotransmitters, such as serotonin, norepinephrine and dopamine, have the ability to affect your mood, emotions and overall feeling of well-being. These chemicals are naturally produced in the brain but may be available in lower quantities in a person with depression. It's these neurotransmitters that are affected by antidepressants.

How Antidepressants Work

Generally, antidepressants work by increasing the concentration of certain neurotransmitters within the brain, which, in turn, improves mood. While there are different types of antidepressants, each one works to manipulate one or more of the brain's neurotransmitters.

For example, tricyclic antidepressants, or TCAs, are a type of antidepressant that work by increasing the concentration of norepinephrine and serotonin. The drug is able to do this because it blocks the reabsorption of the neurotransmitters back into the first communicating neuron. It's as if the TCAs lock the door behind the neurotransmitters once they leave the first neuron.

Since the neurotransmitters cannot go back to the first neuron, they stay in the gap between the nerve cells, therefore increasing the concentration within the gap. The higher concentration of neurotransmitters in the space is thought to push more of the chemical messengers toward the second neuron, which strengthens the communication.

TCAs, along with monoamine oxidase inhibitor antidepressants, or MAOIs, are older families, or types, of antidepressants. MAOIs do not block reabsorption; instead they inhibit the breakdown of the neurotransmitters by stopping the action of an enzyme called monoamine oxidase. Because the neurotransmitters are not broken down, their concentrations are increased within the brain.

While these older antidepressants are both still used today, they are thought to be associated with a high number of side effects, such as weight gain, drowsiness, dizziness, blurred vision, dry mouth, constipation and sexual dysfunction. Newer antidepressants have been developed that seem to lessen, but not eliminate, many of these side effects.

SSRIs and SNRIs

One type of antidepressant that is frequently prescribed today is known as selective serotonin reuptake inhibitors, or SSRIs. As the name describes, SSRIs are able to increase serotonin concentrations in the brain because they inhibit the reabsorption (reuptake) of serotonin back into the first communicating neuron. In other words, when serotonin gets released into the gap between the two communicating cells, it's incapable of going backward. This builds up the concentration within the gap and pushes more serotonin toward the second cell. Because higher serotonin levels are thought to be associated with feeling good, depression is alleviated.

There are additional antidepressants that are fairly new to the market. Each of these works in a similar way as SSRIs, meaning they increase concentrations of neurotransmitters by blocking their reuptake. Which neurotransmitters are affected depends on the antidepressant. Some medications, such as serotonin and norepinephrine reuptake inhibitors, or SNRIs, as their name implies, inhibit the reuptake of serotonin and norepinephrine, while other drugs work by manipulating the reuptake of different combinations of neurotransmitters.

Lesson Summary

Depression is a disorder characterized by feelings of hopelessness, sadness and a lack of interest in life. Antidepressants are drugs that work to prevent and treat depression. Antidepressants work by increasing the concentration of certain neurotransmitters within the brain, which, in turn, improves mood.

Tricyclic antidepressants, or TCAs, work by increasing the concentration of norepinephrine and serotonin. Monoamine oxidase inhibitor antidepressants, or MAOIs, inhibit the breakdown of the neurotransmitters by stopping the action of an enzyme called monoamine oxidase.

Selective serotonin reuptake inhibitors, or SSRIs, inhibit the reabsorption (reuptake) of serotonin back into the first communicating neuron, and serotonin and norepinephrine reuptake inhibitors, or SNRIs, inhibit the reuptake of serotonin and norepinephrine.

Learning Outcomes

As soon as the lesson concludes, apply the knowledge you've accumulated to:

Summary:

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